Method of controlling motor-driven washing machine and control system for the same

ABSTRACT

A method of controlling a motor-driven washing machine and a control system that controls a motor or any other components of the washing machine are disclosed. The method includes the steps of generating an interruption command for braking a motor in motion during a wash cycle, applying a phase-reversed voltage to a voltage input terminal of the motor in motion, and electrically shorting the input terminal of the motor for a predetermined period of time if a second phase-reversed voltage generated by the motor is higher than or equal to a critical voltage level. Using such method, a motor-clutch mechanism is prevented front generating a noise and from being damaged during a wash cycle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Application No.P2002-26886 filed on May 15, 2002, Korean Application No. P2002-27127filed on May 16, 2002, Korean Application No. P2002-27132 filed on May16, 2002, Korean Application No. P2002-40211 filed on Jul. 11, 2002,Korean Application No. P2002-40292 filed on Jul. 11, 2002, KoreanApplication No. P2002-44687 filed on Jul. 29, 2002, Korean ApplicationNo. P2002-73580 filed on Nov. 25, 2002, Korean Application No.P2002-73898 filed on Nov. 26, 2002, Korean Application No. P2002-74052filed on Nov. 26, 2002, and Korean Application No. P2002-74054 filed onNov. 26, 2002, all of which are hereby incorporated by reference as iffully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a washing machine, and moreparticularly, to a method of controlling a motor-driven washing machineand a control system for the same.

2. Discussion of the Related Art

Motor-driven automatic washing machines are common these days. A typicalwashing machine may include a motor for driving an agitator and arotatable tub severing both as a wash tub and a dehydration tub and themotor is coupled to a drive shaft. During a typical wash or rinse cycle,the motor is caused to rotate back and forth to agitate the clothes andwater in the wash tub for cleaning or rinsing of the clothes.

In addition, during a spine cycle, the motor spins the wash tubcontaining a load of wet clothes to be dehydrated to remove water fromthe wet clothes by centrifugal force. Because the wash tub rotates at avery high speed, many problems can occur. For example, if the operationof the motor is not stopped properly when a user mistakenly opens awasher door and sticks a hand into inside of the tub, the user may beseriously harmed. The user should be advised of such error promptly sothat the error of the motor or any other components that associates withthe motor can be quickly fixed.

In another example, when a control for braking a motor in motion duringa spin cycle is not properly done, the motor-clutch mechanism maygenerates a noise and the mechanism can be damaged due to the motion ofthe heavy wash tub at a high speed.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method ofcontrolling a motor-driven washing machine and a control system for thesame that substantially obviate one or more problems due to limitationsand disadvantages of the related art.

An object of the present invention is to provide a method of controllinga motor-driven washing machine and a control system for the same thatprevent a motor-clutch mechanism from generating a noise and beingdamaged.

Another object of the present invention is to provide a method ofcontrolling a motor-driven washing machine and a control system for thesame, in which a proper control can be achieved even if an initialalgorithm for braking a motor is not executed properly.)

Another object of the present invention is to provide a method ofcontrolling a motor-driven washing machine and a control system for thesame in which, malfunction of a motor during a motor interruption isdetermined and a corresponding error message is displayed for warning auser of the malfunction.

Another object of the present invention is to provide a method ofcontrolling a motor-driven washing machine that performs a motorinterruption based on the weight of a load of clothes to be washed ordehydrated.

Another object of the present invention is to provide a method ofcontrolling a motor-driven washing machine and a control system for thesame that prevent a motor from being damaged due to reverse voltagesgenerated by the motor during motor-brake operation.

Another object of the present invention is to provide a method ofcontrolling a motor-driven washing machine and a control system for thesame, in which malfunction of a braking resistor is detected and motoroperation is stopped for avoiding any motor damage.

Another object of the present invention is to provide a method ofcontrolling a motor-driven washing machine and a control system for thesame that minimize the time it takes to reduce the motor speed.

Another object of the present invention is to provide a method ofcontrolling a motor-driven washing machine and a control system for thesame, in which a washer door is locked only when the speed of a motorreaches a predetermined speed.

Another object of the present invention is to provide a method ofcontrolling a motor-driven washing machine and a control system for thesame that prevent the motor from being damaged during a spin cycle.

A further object of the present invention is to provide a circuit forlimiting a motor current in an electrical appliance that the value ofthe limiting current can be varied.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of controlling a motor-driven washing machine includes the stepsof generating an interruption command for braking a motor in motionduring a wash cycle; applying a first phase-reversed voltage to avoltage input terminal of the motor in motion, the first phase-reversedvoltage corresponding to a first current speed of the motor; andelectrically shorting the voltage input terminal of the motor for apredetermined period of time if a second phase-reversed voltage ishigher than or equal to a critical voltage level, the secondphase-reversed voltage corresponding to a second current speed of themotor.

In another aspect of the present invention, a control system for awashing machine includes a motor rotating at least one of a washing tuband an agitator provided in the washing machine in a wash cycle; a motorbrake unit initially applying a first phase-reversed voltage to avoltage input terminal of the motor when an interruption command forbraking the motor in motion is generated during the wash cycle, thefirst phase-reversed voltage corresponding a first current speed of themotor in motion, and a controller measuring a second current speed ofthe motor and generating a control signal if a second phase-reversedvoltage is higher than or equal to a critical voltage level, the secondphase-reversed voltage corresponding to the second current speed of themotor, wherein the motor brake unit electrically shorts the voltageinput terminal of the motor upon receiving the control signal from thecontroller.

In another aspect of the present invention, a method of controlling amotor-driven washing machine having a load controller includes the stepsof initiating a wash cycle by operating a plurality of load unitsincluding a motor according to a wash option selected by a user;transmitting a brake control signal to the load controller if an openingof a washer door provided in the washing machine is detected, the loadcontroller executing a load-brake algorithm to brake operations of theplurality of load units in response to the brake control signal;determining whether the load-brake algorithm is properly executed by theload controller by communicating with the load controller; andtransmitting control signals directly to the plurality of the load unitsso as to brake the operations of the plurality of the load units if theload-brake algorithm is properly executed by the load controller.

In another aspect of the present invention, a control system for awashing machine includes a door sensor detecting an opening of a washerdoor provided in the washing machine; a load controller coupled to thedoor sensor for executing a load-brake algorithm to brake operations ofa plurality of load units of the washing machine when the opening of thewasher door is detected by the door sensor; a main controllertransmitting control signals directly to the plurality of load units soas to brake the operations of the plurality of load units if theload-brake algorithm is not properly executed by the load controller.

In another aspect of the present invention, a method of controlling amotor-driven washing machine includes the steps of initiating a washcycle by operating a motor provided in the washing machine according toa washing option selected by a user; generating a motor-brake signal tobrake the operation of the motor when a motor-interruption command isgenerated and measuring a brake period which represents a total lengthof time it takes to completely stop the operation of the motor;determining malfunction of the motor based on whether the measured brakeperiod exceeds a predetermined period of time; and displaying a warningmessage on a display unit, the message indicating the determinedmalfunction of the motor.

In another aspect of the present invention, a control system for awashing machine includes a motor rotating a washing tub or an agitatorprovided in the washing machine according to a washing option selectedby a user; a microprocessor operatively coupled to the motor for brakingoperation of the motor when a motor-interruption command is generatedand measuring a brake period which represents a total length of time ittakes to completely stop the operation of the motor, the microprocessordetermining malfunction of the motor based on whether the measured brakeperiod exceeds a predetermined period of time; and a display unitdisplaying a warning message indicating the determined malfunction ofthe motor upon receiving a control signal from the microprocessor.

In another aspect of the present invention, a method of controlling amotor-driven washing machine includes the steps of increasing a speed ofa motor from zero to a first predetermined speed W to initiate a spincycle, during which the motor rotates a washing tub containing a load ofclothes to be dehydrated; reducing the motor speed from W₁ to a secondpredetermined speed W₂ and measuring a deceleration period that it takesto reduce the motor speed from W₁ to W₂; increasing the motor speed fromW₂ to a third predetermined speed W₃; braking the motor according to aslow brake logic if a first interruption of the motor is ordered duringthe step of increasing the motor speed from W₂ to W₃; increasing themotor speed from W₃ to a fourth predetermined speed W₄; and selectingone of plurality of rapid-brake logics on the basis of the measureddeceleration period and braking the motor according to the selectedrapid-brake logic if a second interruption of the motor is orderedduring the step of increasing the motor speed from W₃ to W₄.

In another aspect of the present invention, a method of controlling amotor-driven washing machine includes the steps of applying aphase-reversed voltage to a voltage terminal of a motor in motion tobrake the motor when a motor-interruption command is generated during awash or spin cycle, the motor generating a reverse voltage and a reversecurrent when being braked; initially reducing the reverse voltagegenerated by the motor by allowing the reverse current to flow through abraking resistor connected to the motor if the reverse voltage is higherthan a predetermined voltage level; determining malfunction of thebraking resistor on the basis of an actual current-flow period of thebraking resistor; and electrically shorting the voltage terminal of themotor for a predetermined period of time if the malfunction of thebraking resistor is determined.

In another aspect of the present invention, a control system for awashing machine includes a motor rotating a washing tub or an agitatorprovided in the washing machine in a wash or spin cycle; a motor drivingunit applying a phase-reversed voltage to a voltage terminal of themotor in motion if a motor-interruption command is generated, the motorgenerating a reverse voltage and a reverse current when thephase-reversed voltage is applied; a braking resistor connected to themotor; and a microprocessor initially reducing the reverse voltagegenerated by the motor by allowing the reverse current to flow throughthe braking resistor if the reverse voltage is higher than apredetermined voltage level, the microprocessor electrically shortingthe voltage terminal of the motor for a predetermined period of time ifit determines malfunction of the braking resistor on the basis of anactual current-flow period of the braking resistor.

In another aspect of the present invention, a method of controlling amotor-driven washing machine includes the steps of determining whether acurrent DC voltage of a driving unit driving a motor is less than orequal to a predetermined voltage level for each predetermined period;measuring a current leading phase angle of the current DC voltage if thecurrent voltage is less than or equal to the predetermined voltagelevel; and decreasing the current leading phase angle of the current DCvoltage by a first predetermined level if the measured leading phaseangle is greater than zero.

In another aspect of the present invention, a control system for amotor-driven washing machine includes an electrical motor; a drivingunit that applies an input voltage to the motor to drive the motor; avoltmeter that measures a reverse voltage generated by the motor foreach predetermined period; and a microprocessor reducing a speed of themotor if the measured reverse voltage is less than or equal to apredetermined voltage level.

In another aspect of the present invention, a method of controlling amotor-driven washing machine includes the steps of determining whether acommand for a spin cycle is received from a user; and locking a washerdoor on the basis of whether a speed of a motor reaches a firstpredetermined speed if the spin cycle command is received, the motorrotating a washing tub containing a load of clothes to be dehydrated.The step of locking the washer door includes increasing the motor speedfrom zero to the first predetermined speed to initiate the spin cycle;and generating a control signal to a door locking unit if the motorspeed is equal to the first predetermined speed, the door locking unitlocking the washer door upon receiving the control signal.

In another aspect of the present invention, a control system for awashing machine includes a washing tub containing a load of clothes tobe dehydrated; an electrical motor rotating the washing tub if a commandfor a spin cycle is received from a user; and a microprocessor locking awasher door on the basis of whether a speed of the motor reaches a firstpredetermined speed.

In another aspect of the present invention, a method of controlling amotor-driven washing machine includes the steps of determining whether afirst current speed of a motor is less than a first predetermined speedif a motor-interruption of the motor is generated during a spin cycle,the motor rotating a washing tub containing a load of clothes to bedehydrated during the spin cycle; and braking the motor in motion byshorting power terminals of the motor for a first predetermined periodif the first current speed is less than the first predetermined speed.The method further includes the steps of applying phase-reversedvoltages to the power terminals for a second predetermined period if asecond current speed of the motor is less than the first predeterminedspeed and greater than a second predetermined speed; and allowing abraking resistor connected to the motor to flow reverse currentsgenerated by the motor so as to dissipate electrical power into heat ifthe second current speed of the motor is less than the firstpredetermined speed and greater than the second predetermined speed.

In another aspect of the present invention, a control system for awashing machine includes a washing tub containing a load of clothes tobe dehydrated; a motor rotating to the washing tub during a spin cycle;and a microprocessor braking the motor shorting power terminals of themotor if a motor-interruption is generated during the spin cycle and ifa first current speed of the motor is less than a first predeterminedspeed.

In another aspect of the present invention, a circuit for limiting amotor current in an electrical appliance includes a first resistor and adip switch connected between a power source and a ground in series, thedip switch comprising a plurality of resistors having differentresistances; a capacitor connected to the dip switch in parallel; an opamplifier having an inverting input connected to a node between thefirst resistor and the dip switch; and a third resistor connectedbetween an noninverting input of the op amplifier and a ground, whereinany one of the plurality of resistors of the dip switch can beconveniently selected for limiting a current that flows through thethird resistor.

In another aspect of the present invention, a method of controlling amotor-driven washing machine includes the steps of measuring a voltageof a node between the transistor and the braking resistor; displaying awarning message indicating that the brake resistor is in an inoperativecondition if the measured voltage is equal to zero; repeating the stepof determining if a command for a wash cycle is received; and initiatingthe wash cycle if the measured voltage of the node is not equal to zero.

In another aspect of the present invention, a control system for awashing machine includes a motor rotating a wash tub or an agitator ofthe washing machine; a driving unit that drives the motor by applyinginput voltages to the motor; a pair of a braking resistor and atransistor connected to the driving unit in parallel, the transistorbeing connected to the braking resistor in series; a voltmeter measuringa voltage of a node between the transistor and the braking resistor; anda microprocessor generating a warning signal if the measured voltage ofthe node is not equal to zero.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings;

FIG. 1A illustrates a control system that drives a motor provided in awasher according to a first embodiment of the present invention;

FIG. 1B illustrates the detailed structures of the motor brake unit 60,the transformer 50 and the motor 81 shown in FIG. 1A;

FIG. 1C illustrates a current flow (L1) of the motor brake unit 60 whenthe phase-shifted voltage applied to the motor brake unit 60 is lessthan V_(c);

FIG. 1D illustrates a method of controlling a motor provided in a washeraccording to the first embodiment of the present invention;

FIG. 2A illustrates an apparatus of controlling load units (e.g., amotor) in a washer according to a second embodiment of the presentinvention;

FIG. 2B illustrates a method of controlling load units in a washeraccording to the second embodiment of the present invention;

FIG. 3A illustrates an apparatus of detecting malfunction of a motor ina washer according to a third embodiment of the present invention;

FIG. 3B illustrates a method of detecting malfunction of a motor in awasher according to the third embodiment of the present invention;

FIG. 4A and FIG. 4B illustrate a method of interrupting (braking)operation of a motor in a washer according to a fourth embodiment of thepresent invention; FIG. 5A illustrates a control system that drives amotor provided in a washer according to a fifth embodiment of thepresent invention;

FIG. 5B illustrates a method of controlling a motor in a washeraccording to the fifth embodiment of the present invention;

FIG. 6A illustrates a control system that drives a motor provided in awasher according to a sixth embodiment of the present invention;

FIG. 6B illustrates a method of controlling a motor in a washeraccording to the sixth embodiment of the present invention;

FIG. 7A illustrates a control system controlling a motor in a washeraccording to a seventh embodiment of the present invention;

FIG. 7B illustrates a method of controlling a motor in a washeraccording to the seventh embodiment of the present invention;

FIG. 8A illustrates an apparatus of controlling operation of a motor ina washer according to an eighth embodiment of the present invention;

FIG. 8B illustrates a method of controlling operation of a motor in awasher according to the eighth embodiment of the present invention;

FIG. 9A illustrates a control system that drives a motor provided in awasher according to a ninth embodiment of the present invention;

FIG. 9B illustrates a method of controlling a motor in a washeraccording to the ninth embodiment of the present invention; and

FIG. 10 illustrates a circuitry for limiting a motor current in anelectrical appliance according to a tenth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Embodiment (1)

FIG. 1A illustrates a control system that drives a motor provided in awasher according to a first embodiment of the present invention.Referring to FIG. 1A, the control system includes a power supply unit 40rectifying and/or smoothing an AC power voltage generated by a powersource, a transformer 50 having a converter (not illustrated) and forconverting the rectified AC voltage into a DC voltage and a capacitor(not illustrated) for storing the converted DC voltage, a motor 81rotating a tub and/or an agitator provided in the washer, a motor brakeunit 60 braking the operation of the motor 81 by applying an inputvoltage to the motor 81 upon receiving a brake control signal, and acontroller 70 measuring the DC voltage stored by the transformer 50 andgenerating the brake control signal to the motor brake unit 60.

The DC voltage stored in the capacitor of the transformer 50 is used fordriving the motor 81, and the motor 81 transmits the dynamic energy to aclutch (not illustrated) that engages with the tub and/or agitatorprovided in the washer for washing a load of clothes to be washed. Whena user inputs a command for interrupting (braking) the motor operationby turning the power of the washer off, opening a washer door, ormanually touching a key control panel, the controller 70 generates amotor interruption signal to the motor brake unit 60. In addition, thecontroller 70 continuously monitors the speed of the motor 81 andoutputs the motor speed information to the transformer 50, which thenapplies a voltage corresponding to the motor speed to the motor brakeunit 60.

The motor brake unit 60 shifts the phase of the voltage outputted by thetransformer 50 by 180 degrees and applies the phase-shifted voltage(phase-reversed voltage) to the motor 81 so as to brake the motoroperation. However, when a phase-shifted voltage corresponding to aspeed value higher than a certain motor speed is applied to the motor81, a noise may be generated in the motor-clutch mechanism and themechanism may be damaged. This is because the actual rotationaldisplacement of the clutch is greater than the rotational displacementof the motor 81 due to the rotational speed difference between the motor81 and the clutch. For this reason, the controller 70 initially stores acritical phase-shift voltage Vc that starts to generate the noise in themotor-clutch mechanism and that may damage the mechanism, and itperforms a motor brake by shorting the power input terminals of themotor 81 if the current phase-reversed voltage is greater than V_(c).

FIG. 1B illustrates the detailed structures of the motor brake unit 60,the transformer 50 and the motor 81 shown in FIG. 1A. As shown in FIG.1B, the motor brake unit 60 comprises three pairs of insulated gatebipolar transistors (hereinafter, “transistor”) connected in parallel,where each pair comprises two transistors connected in series. A diode(D1 to D6) is connected to each transistor, which can be shorted by thediode. Transistors T2, T4 and T6, which are directly connected to threewinded wires of the motor 81, apply the voltage supplied by thetransformer to the winded wires of the motor 81, respectively, foroperating or braking the motor 81.

FIG. 1C illustrates a current flow (L1) of the motor brake unit 60 whenthe phase-shifted voltage applied to the motor brake unit 60 is lessthan V_(c). On the other hand, a current flow (L2) of the motor brakeunit 60 when the phase-shifted voltage is greater than or equal toV_(c). In other words, if the controller 70 determines that the voltagebeing inputted to motor brake unit 60 is greater than or equal to V_(c),the motor brake unit 60 shorts the input terminals of the motor 81 asshown in FIG. 1B for a predetermined period of time (e.g., 0.5 sec). Asshown in FIG. 1B, the connections between the transformer 50 and themotor 81 are shorted by activating T2, T4 and T6 and D2, D4 and D6 andby deactivating T1, T3, and T5. Therefore, the voltage of thetransformer 50 is not applied, but instead, the voltage previouslyapplied to the winded wires 85 of the motor 81 are consumed for brakingthe motor operation. After the input terminals of the motor 81 areshorted for 0.5 sec, the speed of the motor 81 is reduced and thereduced motor speed is transmitted to the controller 70, which thenapplies a voltage corresponding to the reduced motor speed to the motordriving unit 60 so that the motor 81 can be stopped without generatingany noise in the motor-clutch mechanism.

Reference will now be made in detail to a method of controlling a motorprovided in a washer according to the first embodiment of the presentinvention, which is illustrated in FIG. 1D. Initially, a user inputs acommand for interrupting (braking) the motor operation by turning thepower of the washer off, opening a washer door, or manually touching akey input panel (SS1). Next, the controller 70 controls the transformer50 to apply a voltage corresponding to the current motor speed to themotor brake unit 60, which then performs a motor brake by shifting thephase of the voltage by 180 degrees and applying the phase-shiftedvoltage (phase-reversed voltage) to the motor 81 (S2). Thereafter, thecontroller 70 measures the current speed of the motor 81 again andcompares the voltage corresponding to the measured motor speed with acritical phase-shift voltage Vc (S3), which is previously stored by thecontroller and represents a value of the phase-shifted voltage thatcauses the motor-cutch mechanism to generate a noise if applied to themotor 81.

If the voltage corresponding to the current motor speed is less than Vc,steps S2 and S3 are repeated again. On the other hand, if the voltage isgreater than or equal to Vc, the controller 70 performs a motor brake byshoring the power input terminals of the motor 81 for a predeterminedperiod of time T (e.g., 0.5 sec) so that the voltage corresponding thecurrent motor speed is not applied to the motor 81. Next, if thecontroller 70 determines that the operation of the motor 81 is stopped(S5), it terminates the motor brake algorithm. Otherwise, steps S1 to S5are repeated until the motor operation is stopped.

Embodiment (2)

FIG. 2A illustrates an apparatus of controlling load units (e.g., amotor) in a washer according to a second embodiment of the presentinvention. Referring to FIG. 2A, the apparatus includes a key input unit210 receiving commands from a user for a wash cycle, a door sensor 240for sensing opening of a washer door of the washer, and a loadcontroller 230 that executes an interrupt program or algorithm forinterrupting operations of load units 260 upon receiving a signalindicating the opening of the washer door, where the load units 260include a motor rotating a tub and/or an agitator provided in thewasher, a water supply system supplying water to the tub, and a drainsystem draining water from the tub. The apparatus shown in FIG. 2Afurther includes a main controller 220 that generates control signals toinitiate the wash cycle according to the user's commands and controlsthe operations of the load units based upon whether the interruptprogram is properly executed by the load controller 230. The apparatusfurther includes a memory 250 (e.g., EEPROM) for storing a plurality ofparameter values that correspond to various washing options and adisplay unit 270, such as an LCD display, that displays informationindicating the opening of the washer door upon receiving a controlsignal from the main controller 220.

When a user inputs commands for a wash cycle through the key input unit210, the main controller 220 transmits the commands to the loadcontroller 230. Then the load controller 230 performs a wash cycle bydriving the load units 260 according to the received commands. The loadunits 260 include a motor rotating a tub, and it may further include awater supply supplying water to the tub and a drain draining water fromthe tub.

When the door sensor 240 detects or senses opening of a washer door, itsends a signal indicating the opening of the washer door to the loadcontroller 230 and the main controller 220. Thereafter, the loadcontroller 230 runs an interrupt program (e.g., executing an interruptalgorithm) for interrupting or suspending operations of the load units260. The main controller 220 determines whether the load controller 230has executed the interrupt program properly. If the main controller 220determines that the load controller 230 has not executed the programproperly, it generates a direct control signal to the load units 260 forproperly interrupting or suspending the operations of the load units260. For example, the load controller 230 periodically transmits speed(RPM) information of a motor which is operatively coupled to the loadcontroller 30 so that the main controller 220 can determine whether theload controller 230 has executed the interrupt program properly bymonitoring the speed information of the motor.

Reference will now be made in detail to a method of controlling loadunits in a washer according to the second embodiment of the presentinvention, which is illustrated in FIG. 2B. Referring to FIG. 2B, themain controller 220 initially generates control signals to initiate awash cycle according to a washing option selected by a user (S211). Ifthe main controller 220 detects opening of a washer door during the washcycle (S212), it determines whether the load controller 230 has executedan interruption program (e.g., an interrupt algorithm) properly byreceiving operation data of the load units 260 from the load controller230 via a data communication line, such as a serial communication line,and by monitoring the received operation data (S213). If it isdetermined in step S213 that an interruption program is properlyexecuted by the load controller 230, then the main controller 220 allowsthe load controller to interrupt the operations of the load units 260(S214). On the other hand, if the interrupt program is not properlyexecuted, the main controller 220 sends direct control signals to theload units 260 for interrupting the operations of the load units 260(S215). One of the advantages of controlling the load units of a washeraccording to the second embodiment described above is that a reliablecontrol for interrupting operations of the load units is still achievedeven when any error occurs in interrupting the operations of the loadunits by the load units.

Embodiment (3)

FIG. 3A illustrates an apparatus of detecting malfunction of a motor ina washer according to a third embodiment of the present invention.Referring to FIG. 3A, the apparatus includes a key input unit 310receiving commands from a user for a wash cycle, a motor 340 rotating atub and/or an agitator in the washer, a speed measuring unit 330measuring the speed of the motor 340, and a counter 320 that measuresinterruption periods of the motor 340. An interruption period of themotor 340 represents a period of time that it takes for the motor 340 tocompletely stop since an interruption command is inputted by the userthrough the key input unit 310 or opening of a washer door (notillustrated) of the washer is detected. The apparatus shown in FIG. 3Afurther includes a memory 370 (e.g., EEPROM) that stores the measuredinterruption period of the motor 340 if the measured period is greaterthan a predetermined length of time, a microprocessor 360 thatdetermines malfunction of the motor 340 based upon whether a totalnumber of the stored interruption periods, which are greater than thepredetermined length of time, is greater than a threshold frequency, anda display unit 350 (e.g., an LCD) that indicates the malfunction of themotor 340 upon receiving a control signal from the microprocessor 360.

When the microprocessor 360 receives an interruption command from theuser through the key input unit 310 or detects opening of a washer doorof the washer, it generates an interruption signal to the motor 340 tointerrupt or stop operation of the motor 340. Thereafter, the counter320 measures an interruption period of the motor 340, which represents aperiod of time it takes for the motor 340 to completely stop since theinterruption signal is generated by the microprocessor 360, and themicroprocessor stores the measured interruption period in the memory 370if the measured period is greater than a predetermined length of time.Next, the microprocessor 360 determines whether a total number of theinterruption periods stored in the memory 370 is greater than athreshold frequency. If the total number of periods is determined to bethe threshold frequency, the microprocessor 360 sends a control signalto the display unit 350 to display a message indicating malfunction ofthe motor 340 to the user.

Reference will now be made in detail to a method of detectingmalfunction of a motor in a washer according to the third embodiment ofthe present invention, which is illustrated in FIG. 3B. Referring toFIG. 3B, when power is supplied to a washer (S31) and the microprocessor360 determines that a command for initiating a wash cycle is receivedfrom the user through the key input unit 310 (S32), the microprocessor360 initiates the wash cycle according to a wash option selected by theuser (S33). Thereafter, when the microprocessor 360 determines that aninterruption command is received from the user through the key inputunit 310 or opening of a washer door of the washer is detected (S34), itgenerates an interruption signal to interrupt or stop operation of themotor 340 and measures an interruption period of the motor 340 using thecounter 320 (S36). The interruption period of the motor 340 represents aperiod of time it takes to completely stop the operation of the motor360 since the interruption signal is generated. On the other hand, if itis determined in step S34 that no interruption command is received fromthe user and the opening of the washer door is not detected, themicroprocessor 360 continues the wash cycle (S35).

Referring back to FIG. 3B, after the interruption period of the motor340 is measured in step S36, the microprocessor 360 determines whetherthe measured interruption period is greater than a predetermined lengthof time T_(predetermined) (S37). If it is, it stores the measuredinterruption period in the memory 370 (S38), and otherwise, it finishesinterrupting the operation of the motor 340 (S41). Next, themicroprocessor 360 further determines whether a total number of theinterruption periods, which are stored in the memory 370 up to thepresent time, is greater than a threshold frequency valueN_(predetermined) (S39). If the total number of periods is determined tobe greater than the threshold frequency value in step S39, themicroprocessor 360 sends a display control signal to the display unit350 to display a message indicating malfunction of the motor 340 to theuser (S40). Using the apparatus and method according to the thirdembodiment of the present invention, a user can easily and convenientlybe notified of malfunction of the motor 340 when the operation of themotor is not completely stopped within a predetermined length of timeupon receiving an interruption command from the microprocessor 360.Therefore, the user can repair the motor in advance without damaging themotor or any other component of the washer.

Embodiment (4)

FIG. 4 illustrates a method of interrupting (braking) operation of amotor in a washer according to a fourth embodiment of the presentinvention. The washer includes a motor rotating a tub or an agitator, amicroprocessor generating control signals to control operation of themotor. Referring to FIG. 4, the microprocessor of the washer initiallyincreases the speed of the motor W (S411). When W is determined to begreater or equal to a first predetermined speed W₁ (S412), themicroprocessor turns the motor power off (S413). On the other hand, if Wis determined to be less than W₁ in step S412 and if interruption of themotor operation is ordered (S414), the microprocessor interrupts(brakes) the motor operation based on a slow-brake logic (S415). Theinterruption of the motor operation gets ordered when a user inputs acommand for interrupting (braking) the motor operation by turning thepower of the washer off, opening a washer door, or manually touching akey control panel.

After the motor power is turned off in step S413, power-free rotation ofthe motor occurs and thereby W gradually decreases (S416). If themicroprocessor determines that the microprocessor determines whether Wis less than or equal to a second predetermined speed W₂ being less thanW₁ (S417), it determines the weight of a load of clothes being containedin the tub by measuring T that represents a length of time that it takesfor W to decrease from W₁ to W₂ (S418). On the other hand, if W isdetermined to be still greater than W₂ in step S417 and if interruptionof the motor operation is ordered (S419), step S415 is repeated.

After the load weight is determined in step S418, the microprocessorincreases W (S420). If W is determined to be greater than or equal to athird predetermined speed W₃ which is greater than W₁ (S421), themicroprocessor further increases W (S423). On the other hand, if W isdetermined to be less than W₃ in step S421 and if interruption of themotor operation is ordered (S422), step S415 is repeated. Referring backto step S423, if W is determined to be greater than or equal to a fourthpredetermined speed W₄ which is greater than W₃ (S424), themicroprocessor maintains the motor speed to W₄ and performs a spin cycle(S425).

If W is determined to be less than W₄ in step S424 and if interruptionof the motor operation is ordered (S426), the microprocessor selects oneof a plurality of rapid-brake logics on the basis of T measured in stepS418 and interrupts or brakes the motor operation according to theselected rapid-brake logic (S427-S432). For example, if T is determinedto be less than or equal to a first predetermined length of time T₁(S427), the microprocessor brakes the motor operation based on a firstrapid-brake logic (S428). And if T is determined to be greater than T₁but less than or equal to a second predetermined length of time T₂(S429), the motor operation is interrupted based on a second rapid-brakelogic (S430). In other words, if T is determined to be greater than an(n−1)th predetermined length of time T_(n-1) but less than or equal toan nth predetermined length of time T_(n) where n=2, 3, 4, . . . N(S431), the microprocessor brakes the motor operation based on an nthrapid-brake logic (S432).

Referring back to step S425, if a spin period, during which W₄ ismaintained, is determined to be greater than or equal to a predeterminedperiod of time E (S433), the microprocessor turns off the motor power(S434). On the other hand, if the spin period is determined to be lessthan E in step S433 and if interruption of the motor operation isordered (S435), the microprocessor selects on of the plurality ofrapid-brake logics on the basis of T measured in step S428 andinterrupts the motor operation according to the selected rapid-brakelogic (S427-S432). After the motor power is turned off in step S434, ifthe microprocessor determines in step S436 that W is less than or equalto W₃ and if interruption of the motor operation is ordered (S43.8),step 415 is repeated. In addition, if W is determined to be greater thanW₃ in step S436 and if interruption of the motor operation is ordered(S437), steps S427 to S432 are repeated.

In the method of interrupting operation of the washer motor shown inFIG. 4, an appropriate motor brake logic is selected based on the weightof the load of clothes so that the optimal interruption of the motoroperation can be achieved while avoiding any damage on the motor or anyother components that associate with the motor.

Embodiment (5)

FIG. 5A illustrates a control system that drives a motor provided in awasher according to a fifth embodiment of the present invention.Referring to FIG. 5A, the control system includes a transformer 54having a converter 54A and a first capacitor C₁ for converting the ACpower generated by the AC power source 52 into DC power, a switch 52Aconnecting or disconnecting the AC power source 52 to the transformer54, and a switching mode power supply (SMPS) unit 56 transforming the DCvoltage converted by the transformer 54 into a voltage having apredetermined level.

The motor control system shown in FIG. 5A further includes a relay unit56A which is connected between the SMPS unit 56 and the AC power source52 and cuts off the AC power if its frequency is higher than apredetermined frequency value, a first resistor R₁ connected to therelay unit 56A in parallel, a motor 51 rotating a tub or an agitator inthe washer, a driving circuit 58 driving the motor 51 by supplying thevoltage converted by the SMPA unit 56 to the motor 51, a microprocessor59 controlling operation of the motor 51, an insulated gate bipolartransistor (IGBT) 57 performing pulse width modulation upon receiving acontrol signal from the microprocessor 59, a voltage comparator 53comparing the reverse voltage generated by the motor 51 during a motorbrake with a predetermined voltage value, and a braking resistor 55dissipating the reverse voltage generated by the motor 51 into heat soas to prevent possible circuit damages due to the reverse voltage.

Reference will now be made in detail to a method of controlling a motorin a washer according to the fifth embodiment of the present invention,which is illustrated in FIG. 5B. Referring to FIG. 5B, when themicroprocessor 59 determines that any one of the conditions for brakingoperation of the motor 51 is met, it sends interruption signals to themotor driving circuit 58, which then applies phase-reversed inputvoltages to the motor 51 (S511). In step S511, the reverse voltages arethen generated by the motor 51 due to its rotation and they are appliedto the driving circuit 58. In a case where the motor 51 is driven bythree input voltages having three different phases, the reverse voltagesgenerated by the motor 51 during the motor brake also have three phases.Therefore, the phases of the reverse voltages depend on the phases ofthe input voltages that the driving circuit 58 applies to the motor 51.

After the reverse voltages are generated by the motor 51 in step S51,the microprocessor 59 measures the reverse voltages generated in stepS511 and determines whether the measured reverse voltages are greaterthan a predetermined voltage value V₁ (S512). If they are, themicroprocessor 59 generates control signals for a normal motor brake, inwhich the braking resistor 55 is allowed to dissipate energy due to thereverse voltages generated by the motor 51 into heat (S513). Otherwise,steps S511 and S512 are repeated until the reverse voltages aredetermined to be greater than V₁.

Next, the microprocessor 59 measures a current-flow period of thebraking resistor 55 which represents a length of time that a reversecurrent flows through the braking resistor 55 when the reverse voltagesare generated by the motor 51, and it further determines whether themeasured current-flow period is less than a normal dissipate period T₁(S514). T₁ represents a period of time that it takes to dissipate allthe reverse voltages by the braking resistor 55 in a normal condition.If the measured current-flow period is less than T₁, the microprocessor59 determines that the braking resistor 55 is opened.

If the measured current-flow period is determined to be not less thanthe T₁, the microprocessor 59 determines whether the measuredcurrent-flow period is greater than T₁ (S515). If the measuredcurrent-flow period is greater than T₁, it determines that the brakingresistor 55 is shorted. If it is determined that the measuredcurrent-flow period is less than or greater than T₁ in step S514 orS515, the microprocessor 59 shorts a corresponding node connected to thedriving circuit 58 for a predetermined period of time so as to reducethe reverse voltages generated by the motor 51 (S516). When the nodeconnected to the driving circuit 58 is shorted, the reverse voltages ofthe motor 51 are reduced due to their phase differences. By doing so,any circuit damage caused by high reverse voltages of the motor 51 canbe prevented during the motor brake.

After the reverse voltages are reduced in step S516 or the measuredcurrent-flow period of the braking resistor 55 is determined to be notgreater than T₁ in step S515, the microprocessor 59 measures the reversevoltages of the motor 51 again and determines whether the measuredreverse voltages are less than the predetermined voltage value V₁(S517). If they are, the microprocessor 59 terminates the operation ofthe motor 51 (S518).

Embodiment (6)

FIG. 6A illustrates a control system that drives a motor provided in awasher according to a sixth embodiment of the present invention. Asshown in FIG. 6A, the system includes a rectifier 611 rectifying the ACpower, a motor 612 rotating a tub or an agitator of the washer, and adriving circuit 613 comprising a plurality of insulating gate bipolartransistors (IGBT). The driving circuit 613 applies input voltages U, V,and W having three different phases, respectively, to the motor 612 in afirst operation mode and applies phase-reversed voltages to the motor612 in a second operation mode so that the reverse voltages generated bythe motor 612 due to its rotation are applied to the driving circuit613.

The system shown in FIG. 6A further includes a switching mode powersupply (SMPS) unit 614 transforming the output of the rectifier 611 intoa voltage having a predetermined level (e.g., 5V), a speedometer 615measuring the rotational speed of the motor 612, a braking resistorR_(b) dissipating the reverse voltages generated by the motor 612 intoheat so as to prevent possible circuit damages, and a transistor T₁driving the braking resistor R_(b). The system further includes avoltmeter 616 that measures the output voltage of the rectifier 611after the reverse voltage of the motor 612 is dissipated in R_(b), adriver microprocessor 617 controlling operations of the driving circuit613 and the transistor T₁ on the basis of the output voltage measured bythe voltmeter 616, a door opening sensor (not illustrated) detectingopening of a washer door and sending a corresponding signal to the drivemicroprocessor 617, a user interface unit 618 having at least one atouch panel and a key input unit for receiving operational commands froma user, a display unit (e.g., LCD) 619 displaying a message indicatingthe operation status of the washer, a sound generating unit 620, and amain microprocessor 621 controlling the drive microprocessor 617 so asto operate various components of the washer including the motor 612according to the operational commands received by the user interfaceunit 618.

The main microprocessor unit 621 detects an abnormal output voltage ofthe rectifier 611 by communicating with the drive microprocessor 617 andgenerates control signals to the display unit 619 and the soundgenerating unit 620 so as to display a warning message and a warningsound indicating the abnormal output voltage of the rectifier 611.Because the brake resistor R_(b) is detachably provided in the controlsystem as shown in FIG. 6A and the voltmeter 616 measures the outputvoltage of the rectifier 611 using R_(b), the output voltage of thevoltmeter 616 will be 0V if R_(b) is not provided at all or theconnector 622 is inoperatively provided.

Reference will now be made in detail to the operation of the controlsystem shown in FIG. 6A. When a user inputs commands for a wash cyclethrough the user through interface unit 618, the main microprocessor 621transmits control signals to the drive microprocessor 617 so as to drivevarious components of the washer based on a plurality of operationparameters corresponding to a wash option selected by the user. Thedrive microprocessor 617 initially rotates the motor 612 whilemonitoring the speed of the motor 612 and performs the wash cycle byoperating other components such as a water supply system and a waterdrain system. On the other hand, the main microprocessor 621 generatescontrol signals to the display unit 619 for displaying a currentoperation status of the washer and to the sound generating unit 620 forgenerating a warning sound if necessary.

During a wash cycle, the rotational direction of the motor 612alternates between a clockwise direction and a counter-clockwisedirection. For example, in order to switch the direction of the motor612 which was initially rotating in a clockwise direction in a firstmode, the rotation of the motor 612 must be initially stopped. Inaddition, such brake or interruption of the motor operation is oftennecessary when a washer door is opened by a user during a spin(dehydration) cycle. Therefore, when the drive microprocessor 617determines that any one of the conditions for braking the motoroperation is met, it operates the driving circuit 613 in a secondoperation mode, in which the driving circuit 613 applies phase-reversedinput voltages to the motor 612 and the brake resistor R_(b) operates todissipates the reverse voltage generated by the motor 611 so as toprevent any circuit damages.

FIG. 6B is a flow chart illustrating a method of controlling a motor ina washer according to the sixth embodiment of the present invention.Initially, the drive microprocessor 617 measures the output voltage ofthe rectifier 611 using the voltmeter 616 (S61). Next, if the drivemicroprocessor 617 determines that the measured output voltage is 0V(S62), it transmits to the main microprocessor 621 a warning signalindicating that the brake resistor R_(b) is not connected at all or isimproperly connected. Because the voltmeter 611 measures the outputvoltage of the rectifier 611 passing through R_(b) using a pair ofresistors R₁ and R₂ connected in series, the measured voltage of 0Vindicates that the power source voltage is being applied but R_(b) isimproperly connected.

Upon receiving the warning signal from the drive microprocessor 617, themain microprocessor 621 generate controls signals to the display unit619 and the sound generating unit 620 for displaying a warning messageindicating R_(b) is improperly connected and for generating a warningsound (S63). If it is determined in step S62 that the output voltage isnot 0V, step S63 is skipped. Next, if the main microprocessor 621determines that operational commands for a wash cycle are inputted by auser through the user interface unit 618 (S64), it further measures theoutput voltage of the rectifier 611 using the voltmeter 616 anddetermines whether the measured output voltage is ON (S65). If it is,the main microprocessor does not initiate the wash cycle but repeatsstep S65 after being in a standby mode for a predetermined period oftime. This step is essentially important for preventing any chance ofdamaging the control system shown in FIG. 6A.

On the other hand, if it is determined in step S65 that the measuredoutput voltage is not 0V (meaning that R_(b) is now properly connected),the main microprocessor 621 initiates the wash cycle by generatingcontrol signals to the drive microprocessor 617 so as to operate variouscomponents of the washer including the motor 621 according to theoperational commands received from the user (S26).

Embodiment (7)

FIG. 7A illustrates a control system controlling a motor in a washeraccording to a seventh embodiment of the present invention. Referring toFIG. 7A, the control system includes a motor 71 rotating a tub or anagitator of the washer, a transformer 72 generating a DC power voltage,and a motor driving unit 73 driving the motor 71 by applying the DCpower voltage to the motor 71. The control system shown in FIG. 7Afurther includes a timer 74 counting a predetermined decelerationperiod, a voltmeter 75 measuring the reverse voltages generated due toreverse currents generated by the motor 71 when interrupted, and amicroprocessor 76 that generates a control signal to the driving unit 71to decrease the motor speed if the measured reverse voltages are lessthan a predetermined voltage value.

The microprocessor 76 initially accelerates the motor speed and controlsthe timer 74 to repeatedly count a predetermined deceleration period soas to reduce the initially accelerated motor speed for each decelerationperiod. In addition, the, microprocessor 76 measures the DC inputvoltage of the motor driving unit 71 for each deceleration period andmaintains a standby status to reduce the input voltage of the drivingcircuit 71 if the measured input voltage is higher than a predeterminedvoltage level. The voltmeter 75 is connected to the DC link in paralleland includes three resistors which are connected in series. Therefore,the output of the voltmeter 75 is a voltage subdivided by the resistorsof the voltmeter 75.

On the other hand, if the measured DC voltage of the driving unit 71 isless than the predetermined voltage level, the microprocessor 76measures the current leading phase angle Φ and reduces the motor speedby reducing the leading phase angel by a predetermined rate for eachdeceleration period. If the leading phase angle d) becomes zero, themicroprocessor 76 obtains the current pulse width modulation (PWM) dutyand reduces the motor speed by reducing the PWM duty by a predeterminedrate for each deceleration period.

Reference will now be made in detail to a method of controlling a motorin a washer according to the seventh embodiment of the presentinvention, which is illustrated in FIG. 7B. When the algorithm shown inFIG. 7B starts, the microprocessor 76 sends to a control signal to thetimer 74 to start measure a time T and determines whether apredetermined deceleration period T_(c) is elapsed by checking whether Tis greater than T_(c) (S701). If T_(c) is elapsed, the microprocessor 76initializes the timer 74 by setting T to zero (S702) and determineswhether the current DC voltage V of the driving unit 71 is less than orequal to a predetermined voltage level V_(c) (S703). If it is determinedin step S703 that V V_(c), then the microprocessor 76 measures thecurrent leading phase angle Φ of the DC voltage V of the driving unit 71(S704). If the measured leading phase angle Φ is greater than zero(S705), the microprocessor 76 reduces the leading phase angle Φ by apredetermined level α (S706). Thereafter, if the microprocessor 76determines that the motor 71 is not stopped (S711), step S701 and allthe following steps are repeated again as shown in FIG. 7B.

On the other hand, if it is determined in step S705 that the measuredleading phase angle Φ is not greater than zero, the microprocessor 76further determines whether the measured leading phase angle Φ is equalto zero (S707). If it is equal to zero, the microprocessor 76 obtainsthe current PWM duty (S708). If the current PWM duty is greater thanzero (S709), it reduces the PWM duty by a predetermined level β. Next,if it determines that the motor is not stopped (S711), all the previoussteps are repeated again. In addition, if it is determined in step S704that the measured DC voltage V is greater than V_(c), steps S704 to S719are skipped and step S711 is performed.

Embodiment (8)

FIG. 8A illustrates an apparatus of controlling operation of a motor ina washer according to an eighth embodiment of the present invention.Referring to FIG. 8A, the apparatus includes a key input unit 810receiving commands from a user for a wash cycle, a motor 830 rotating atub and/or an agitator of the washer, and a controller 820 generatingcontrol signals to perform the wash cycle according to a wash optionselected by the user and to lock a wash door (not illustrated) if thespeed of the motor 830 is equal to a predetermined speed. The apparatusshown in FIG. 8A further includes a washer door locking unit 850 thatlocks or unlocks the washer door of the washer, a speed measuring unit(e.g., a speedometer) 840 measuring the rotating speed of the motor 830and providing the measured speed to the controller 820, and a displayunit 860 that displays a message indicating the locking status of thewasher door upon receiving a control signal from the controller 820.

When a user inputs commands for a wash cycle through the key input unit810, the controller 820 generate control signals to perform a washcycle, a rinse cycle, and a spin (dehydration cycle). After the spincycle is initiated, the controller 820 generates a control signal to thewash door locking unit 850 to lock the washer door when the speed of themotor 830 reaches a first predetermined motor speed. When the speed ofthe motor further reaches a second predetermined motor speed, thecontroller 820 maintains the speed of the motor 830 until the spin cycleis finished.

Reference will now be made in detail to a method of controllingoperation of a motor in a washer according to the eighth embodiment ofthe present invention. Referring to FIG. 5B, if the controller 820determines that a spin cycle (dehydration cycle) is ordered (S801), itincreases the speed W of the motor 830 (S802). Next, if the controller820 determines that W is equal to a first predetermined motor speed W₁,e.g., 700 RPM (S803), it sends a control signal to the washer doorlocking unit 850 to lock the washer door of the washer (S804). If W isdetermined to be less than W₁ in step S803, the controller 820 repeatsstep S802 until W becomes W₁. After the washer door is locked in stepS804, the controller 820 further increases the motor speed W (S805). Ifit is determined that W has reached a second predetermined motor speedW₂, e.g., 1000 RPM, which is greater than W₁ (S806), the controller 820maintains the motor speed W until the spin cycle is finished (S807 andS808). As described above, the controller 820 does not lock the washerdoor until the speed of the motor 830 reaches to the first predeterminedmotor speed W₁ so that the power consumption and durability of the doorlock are greatly improved.

Embodiment (9)

FIG. 9A illustrates a control system that drives a motor provided in awasher according to a ninth embodiment of the present invention. Themotor control system shown in FIG. 9A illustrates a rectifier 911rectifying the AC power, a motor 912 rotating a tub or an agitator ofthe washer, and a driving circuit 913 comprising a plurality ofinsulating gate bipolar transistors (IGBT). The driving circuit 913applies input voltages U, V, and W having three different phases,respectively, to the motor 912 in a first mode and appliesphase-reversed voltages to the motor 912 in a second mode so that thereverse voltages generated by the motor 912 due to its rotation areapplied to the driving circuit 913.

The control system shown in FIG. 9A further includes a switching modepower supply (SMPS) unit 914 transforming the output of the rectifier911 into a voltage having a predetermined level (e.g., 5V), aspeedometer 915 measuring the rotational speed of the motor 912, abraking resistor R_(b) dissipating the reverse voltages generated by themotor 912 into heat so as to prevent possible circuit damages, and atransistor T₁ driving the braking resistor R_(b). The control systemfurther includes a voltmeter 916 measuring the output voltage of therectifier 911 after the reverse voltages of the motor 912 are dissipatedin R_(b), a microprocessor 917 controlling operations of the drivingcircuit 913 and the transistor T₁ on the basis of the output voltagemeasured by the voltmeter 916, and a door opening sensor (notillustrated) detecting opening of a washer door and sending acorresponding to the microprocessor 917.

Reference will now be made in detail to a method of controlling a motorin a washer according to the ninth embodiment of the present invention,which is illustrated in FIG. 9B. Referring to FIG. 9B, when a userinputs commands for washing a load of clothes to be washed, themicroprocessor 917 operates the driving circuit 913 so as to rotate themotor 912 based on a wash algorithm or program that correspond to theuser input commands so that a tub and an agitator of the washer arerotated for performing wash and rinse cycles. Thereafter, themicroprocessor 917 initiates a spin (dehydration) cycle by increasingthe speed of the motor 912 (S931). The speed of the motor 912 in a spincycle should be determined based on a total weight of the load ofclothes to be dehydrated or weight distribution of the load, but istypically greater than 100 rpm.

After a spin cycle is initiated in step S931, the microprocessor 917determines whether a motor brake is necessary by determining any one ofthe conditions for braking motor operation is met (S932). For example,if a motor interruption command inputted by a user or a signalindicating opening of a washer door is received, or if the speed of themotor 912 measured by the speedometer 915 is determined to be abnormal,the microprocessor 917 determines that interruption (brake) of the motoroperation is necessary. If any one of such conditions is met, themicroprocessor 917 determines whether the current speed W of the motor912 is greater than a first critical speed W₁ (S933). W₁ (typically setto 1000 rpm) represents the minimum speed of the motor 912 that canmechanically damage the motor 912 or any other components that associatewith the motor 912 (e.g., a clutch) when a rapid brake of the motoroperation is performed. If it is determined in step S933 that W isgreater than W₁, the microprocessor 917 controls the driving circuit 913to short power input terminals of the motor 912 for a predeterminedperiod of time in order to brake the motor operation (S934). By doingso, rather a slow motor brake is achieved so that any mechanical damagedue to a rapid motor brake can be prevented.

Next, the microprocessor 917 further determines whether the currentspeed W of the motor 912 is less than W₁ and is greater than a secondcritical speed W₂ (S935). W₂ (typically set to 100 rpm) represents theallowable speed of the motor 912 that does not create any mechanicaldamage even if a rapid brake of the motor operation is performed. If itis determined in step S935 that W is less than W₁ and is greater thanW₂, then microprocessor 917 performs a rapid motor brake by operatingthe driving circuit 913 to apply phase-reversed voltages to the motor912 for a predetermined period of time and by operating the brakeresistor R_(b) so as to dissipate the reverse voltages generated by themotor 912 during the rapid motor brake (S936). In the method shown inFIG. 9B, a same rapid brake is performed when W is in a signal speedrange of W₁ to W₂. However, different rapid brakes can be performed fora plurality of subdivided ranges of the motor speed by using differentduty rations when applying the phase-reversed voltages to the motor 912.

Furthermore, the microprocessor 917 further determines whether thecurrent speed W of the motor 912 is less than W₂ (S937). If it is, themicroprocessor 917 controls the driving circuit 913 to short the powerinput terminals of the motor 912 in order to brake the motor operation(S938). Since W is less than 100 rpm, the motor operation can be easily.Thereafter, if the microprocessor 917 determines that the motoroperation is terminated (S939), then it ends the motor controlalgorithm. Otherwise, steps S933 to S939 are repeated.

Referring back to step S932, if none of the conditions for braking motoroperation are met and if the spin cycle is determined to be terminatedin step S940, the microprocessor 917 ends the motor control algorithm.

Embodiment (10)

FIG. 10 illustrates a circuitry for limiting a motor current in anelectrical appliance according to a tenth embodiment of the presentinvention. Referring to FIG. 10, the current limiting circuitry includesa microprocessor 999, a power source V_(cc) supplying a source voltageof 5V, a first resistor R (having a resistance of 33 k and a dip switch997 connected between the power source V_(cc) and a ground in series, acapacitor C₁ connected to the dip switch 997 in parallel, an op amp 998having an inverting input connected to a node between R1 and the dipswitch 997 and an output connected to the microprocessor 999, and athird resistor R₃ having a resistance of 0.027 k, which is connectedbetween the noninverting input of the op amp 998 and a ground.

Reference will now be made in detail to the operation of the currentlimiting circuitry shown in FIG. 10. The dip switch 997 comprises aplurality of resistors having different resistances (e.g., 1.3 k, 1.5 k,1.8 k, 2.0 k, and so on). Therefore, an appropriate one of the pluralityof resistors can be conveniently selected for selecting a limitedcurrent value. For example, if a resistor having a resistance of 1.3 kis selected by the dip switch 997, then the limited current that flowsthrough R3 isI={(5*1.3)/(33÷1.3)}/0.027=7 A.

Alternatively, if a resistor having a resistance of 1.8 k is selected bythe dip switch 997, the limited current that flows through R3 isI={(5*1.8)/(33÷1.8)}/0.027=9A.

As shown in the examples shown above, the value of the limited currentthat flows through R3 is varied based on the switching of the dip switch997. When more than one resistors are selected by the dip switch 997,the value of the current that flows through R3 can be even lower sincethe selected resistors are in parallel. Instead of using the dip switch997, a resistance-variable resistor can be used. However, it has adisadvantage that it is difficult to set a precise resistance value ofthe resistance-variable resistor.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of controlling a motor-driven washing machine, the method comprising the steps of: generating an interruption command for braking a motor in motion during a wash cycle; applying a first phase-reversed voltage to a voltage input terminal of the motor in motion, the first phase-reversed voltage corresponding to a first current speed of the motor; and electrically shorting the voltage input terminal of the motor for a predetermined period of time if a second phase-reversed voltage is higher than or equal to a critical voltage level, the second phase-reversed voltage corresponding to a second current speed of the motor.
 2. The method of claim 1, wherein the interruption command is generated when a user cuts off a power supply to the washing machine, manually touches a key control panel, or opens a washer door of the washing machine during the wash cycle.
 3. The method of claim 1, wherein the critical voltage level is predetermined such that the motor generates a brake noise if the second phase-reversed voltage is higher than or equal to the critical voltage level and is applied to the voltage input terminal of the motor.
 4. The method of claim 1, further comprising the step of applying a third phase-reversed voltage to the voltage input terminal of the motor in motion if the second current speed of the motor is lower than the critical voltage value, wherein the third phase-reversed voltage corresponds to a third current speed of the motor in motion.
 5. The method of claim 1, further comprising the step of applying a third phase-reversed voltage to the voltage input terminal of the motor in motion if the motor is still in motion after the step of electrically shorting the voltage input terminal, wherein the third phase-reversed voltage corresponds to a third current speed of the motor in motion.
 6. A control system for a washing machine, the system comprising: a motor rotating at least one of a washing tub and an agitator provided in the washing machine in a wash cycle; a motor brake unit initially applying a first phase-reversed voltage to a voltage input terminal of the motor when an interruption command for braking the motor in motion is generated during the wash cycle, the first phase-reversed voltage corresponding a first current speed of the motor in motion, and a controller measuring a second current speed of the motor and generating a control signal if a second phase-reversed voltage is higher than or equal to a critical voltage level, the second phase-reversed voltage corresponding to the second current speed of the motor, wherein the motor brake unit electrically shorts the voltage input terminal of the motor upon receiving the control signal from the controller.
 7. The control system of claim 6, further comprising: a power supply generating an AC power voltage; and a transformer converting the AC power voltage into a DC power voltage and supplying the converted DC voltage to the motor brake unit in order to drive the motor.
 8. The control system of claim 6, wherein the interruption command is generated when a user cuts off a power supply to the washing machine, manually touches a key control panel, or opens a door of the washing machine during the wash cycle.
 9. The control system of claim 6, wherein the critical voltage level is predetermined such that the motor generates a brake noise if the second phase-reversed voltage is higher than or equal to the critical voltage level and is applied to the voltage input terminal of the motor.
 10. The control system of claim 6, wherein the motor brake unit further applies a third phase-reversed voltage to the voltage input terminal of the motor if the second current speed is lower than the critical voltage value, the third phase-reversed voltage corresponding to a third current speed of the motor in motion.
 11. A method of controlling a motor-driven washing machine having a load controller, the method comprising the steps of: initiating a wash cycle by operating a plurality of load units including a motor according to a wash option selected by a user; transmitting a brake control signal to the load controller if an opening of a washer door provided in the washing machine is detected, the load controller executing a load-brake algorithm to brake operations of the plurality of load units in response to the brake control signal; determining whether the load-brake algorithm is properly executed by the load controller by communicating with the load controller; and transmitting control signals directly to the plurality of the load units so as to brake the operations of the plurality of the load units if the load-brake algorithm is properly executed by the load controller.
 12. The method of claim 11, wherein the plurality of load units comprises at least one of a motor rotating a washing tub or an agitator provided in the washing machine, a water supply unit supplying water to the tub, and a drain unit draining water from the tub.
 13. The method of claim 11, wherein the step of determining includes the steps of: receiving operation information of the plurality of load units from the load controller; and analyzing the received operation information of the plurality of the load units in order to determine whether the load-brake algorithm is properly executed by the load controller.
 14. The method of claim 13, wherein the operation information includes speed information of the motor.
 15. The method of claim 13, wherein the operation information of the plurality of load units is received from the load controller through a serial data communication line connected to the load controller.
 16. A control system for a washing machine, the system comprising: a door sensor detecting an opening of a washer door provided in the washing machine; a load controller coupled to the door sensor for executing a load-brake algorithm to brake operations of a plurality of load units of the washing machine when the opening of the washer door is detected by the door sensor; a main controller transmitting control signals directly to the plurality of load units so as to brake the operations of the plurality of load units if the load-brake algorithm is not properly executed by the load controller.
 17. The controller system of claim 16, further comprising a display unit displaying an error message indicating that the execution of the load-brake algorithm by the load controller has failed.
 18. The control system of claim 16, wherein the plurality of load units comprises at least one of a motor rotating a washing tub or an agitator provided in the washing machine, a water supply unit supplying water to the tub, and a drain unit draining water from the tub.
 19. The control system of claim 16, wherein the main controller receives operation information of the plurality of load units from the load controller and analyzes the received information in order to determine whether the load-brake algorithm is properly executed by the load controller.
 20. The control system of claim 19, wherein the main controller receives the operation information of the plurality of load units through a serial data communication line connected between the load controller and the main controller.
 21. A method of controlling a motor-driven washing machine, the method comprising the steps of: initiating a wash cycle by operating a motor provided in the washing machine according to a washing option selected by a user; generating a motor-brake signal to brake the operation of the motor when a motor-interruption command is generated and measuring a brake period which represents a total length of time it takes to completely stop the operation of the motor; determining malfunction of the motor based on whether the measured brake period exceeds a predetermined period of time; and displaying a warming message on a display unit, the message indicating the determined malfunction of the motor.
 22. The method of claim 21, wherein the determining step comprises the steps of: storing the measured brake period in a memory if the measured brake period exceeds the predetermined period of time; determining whether a total number of brake periods stored in the memory until the present time is greater than a threshold frequency value; determining the malfunction of the motor if the total number of the stored brake periods is greater than the threshold frequency value.
 23. The method of claim 21, wherein the motor-interruption command is generated when the user manually touches a key control panel or opens a washer door of the washing machine during the wash cycle.
 24. The method of claim 21, further comprising the step of continuing the wash cycle according to the washing option selected by the user if the measured brake period is less than the predetermined period of time.
 25. The method of claim 21, wherein the initiating step includes the step of rotating the motor so as to rotate a washing tub or an agitator provided in the washing machine according to the washing option selected by the user.
 26. A control system for a washing machine, the control system comprising: a motor rotating a washing tub or an agitator provided in the washing machine according to a washing option selected by a user; a microprocessor operatively coupled to the motor for braking operation of the motor when a motor-interruption command is generated and measuring a brake period which represents a total length of time it takes to completely stop the operation of the motor, the microprocessor determining malfunction of the motor based on whether the measured brake period exceeds a predetermined period of time; and a display unit displaying a warning message indicating the determined malfunction of the motor upon receiving a control signal from the microprocessor.
 27. The control system of claim 26, further comprising a memory storing the measured brake period if the measured brake period exceeds the predetermined period of time.
 28. The control system of claim 27, wherein the microprocessor determines the malfunction of the motor if a total number of brake periods that are stored in the memory until the present time is greater than a threshold frequency value.
 29. The control system of claim 27, wherein the memory is an EEPROM and the display unit is an LCD.
 30. The control system of claim 26, further comprising a timer that measures the total length of time it takes to completely stop the operation of the motor.
 31. A method of controlling a motor-driven washing machine, the method comprising the steps of: increasing a speed of a motor from zero to a first predetermined speed W₁ to initiate a spin cycle, during which the motor rotates a washing tub containing a load of clothes to be dehydrated; reducing the motor speed from WV to a second predetermined speed W₂ and measuring a deceleration period that it takes to reduce the motor speed from W₁ to W₂; increasing the motor speed from W₂ to a third predetermined speed W₃; braking the motor according to a slow brake logic if a first interruption of the motor is ordered during the step of increasing the motor speed from W₂ to W₃; increasing the motor speed from W₃ to a fourth predetermined speed W₄; and selecting one of plurality of rapid-brake logics on the basis of the measured deceleration period and braking the motor according to the selected rapid-brake logic if a second interruption of the motor is ordered during the step of increasing the motor speed from W₃ to W₄.
 32. The method of claim 31, wherein the step of reducing the motor speed from W₁ to W₂ is achieved by cutting off a power supply to the motor in motion.
 33. The method of claim 31, further comprising the steps of: maintaining the motor speed of W₄ for a predetermined spin period; and braking the motor according to the selected rapid-brake logic if a third interruption of the motor is ordered during the step of maintaining the motor speed of W₄.
 34. The method of claim 31, further comprising the steps of: reducing the motor speed from W₄ to zero to terminate the spin cycle; and braking the motor in motion according to the selected rapid-brake logic if a third interruption of the motor is ordered during the step of reducing the motor speed from W₄ to zero and if the motor speed is greater than W₃.
 35. The method of claim 34, further comprising the step of braking the motor according to the slow brake logic if the third interruption of the motor is ordered during the step of reducing the motor speed from W₄ to zero and if the motor speed is less than or equal to W₃.
 36. The method of claim 34, wherein the step of reducing the motor speed from W₄ to zero is achieved by cutting off a power supply to the motor in motion.
 37. The method of claim 31, further comprising the step of braking the motor according to the slow brake logic if a third interruption of the motor is ordered during the step of increasing the motor speed from zero to W₁.
 38. The method of claim 31, further comprising the step of braking the motor according to the slow brake logic if a third interruption of the motor is ordered during the step of reducing the motor speed from W₁ to W₂.
 39. The method of claim 31, wherein the first interruption of the motor is ordered when a user inputs a motor-interrupting command by turning the power of the washing machine, opening of a washer door, or manually touching a key control panel during the step of increasing the motor speed from W₂ to W₃.
 40. The method of claim 31, wherein the second interruption of the motor is ordered when a user inputs a motor-interrupting command by turning the power of the washing machine, opening of a washer door, or manually touching a key control panel during the step of increasing the motor speed from W₃ to W₄.
 41. A method of controlling a motor-driven washing machine, the method comprising the steps of: applying a phase-reversed voltage to a voltage terminal of a motor in motion to brake the motor when a motor-interruption command is generated during a wash or spin cycle, the motor generating a reverse voltage and a reverse current when being braked; initially reducing the reverse voltage generated by the motor by allowing the reverse current to flow through a braking resistor connected to the motor if the reverse voltage is higher than a predetermined voltage level; determining malfunction of the braking resistor on the basis of an actual current-flow period of the braking resistor; and electrically shorting the voltage terminal of the motor for a predetermined period of time if the malfunction of the braking resistor is determined.
 42. The method of claim 41, the step of determining malfunction comprises: determining the malfunction of the braking resistor if the actual current-flow period of the braking resistor is less than a normal current-flow period; and determining the malfunction of the braking resistor if the actual current-flow period of the braking resistor is greater than the normal current-flow period.
 43. The method of claim 42, wherein the normal current-flow period is predetermined to represent a length of time that it takes to flow the reverse current through the braking resistor that operates in a normal condition.
 44. The method of claim 41, further comprising the step of further reducing the initially reduced reverse voltage by further allowing the reverse current to flow through the braking resistor if the malfunction of the motor is not deter-mined.
 45. The method of claim 41, further comprising the step of repeating the step of applying the phase-reversed voltage if the reverse voltage is less than or equal to the predetermined voltage level.
 46. A control system for a washing machine, the control system comprising: a motor rotating a washing tub or an agitator provided in the washing machine in a wash or spin cycle; a motor driving unit applying a phase-reversed voltage to a voltage terminal of the motor in motion if a motor-interruption command is generated, the motor generating a reverse voltage and a reverse current when the phase-reversed voltage is applied; a braking resistor connected to the motor; and a microprocessor initially reducing the reverse voltage generated by the motor by allowing the reverse current to flow through the braking resistor if the reverse voltage is higher than a predetermined voltage level, the microprocessor electrically shorting the voltage terminal of the motor for a predetermined period of time if it determines malfunction of the braking resistor on the basis of an actual current-flow period of the braking resistor.
 47. The control system of claim 46, wherein the microprocessor determines the malfunction of the braking resistor if the actual current-flow period is not equal to a normal current-flow period.
 48. The control system of claim 47, wherein the normal current-flow period is predetermined to represent a length of time it takes to flow the reverse current through the braking resistor that operates in a normal condition.
 49. The control system of claim 46, wherein the microprocessor further reduces the initially reduced reverse voltage by further allowing the reverse current to flow through the braking resistor if the actual current-flow period is equal to a normal current-flow period.
 50. The control system of claim 46, wherein the microprocessor generates a control signal to the motor driving unit to further apply the phase-reversed voltage to voltage terminal of the motor if the reverse voltage is less than or equal to the predetermined voltage level.
 51. A method of controlling a motor-driven washing machine, the method comprising the steps of: (a) determining whether a current DC voltage of a driving unit driving a motor is less than or equal to a predetermined voltage level for each predetermined period; (b) measuring a current leading phase angle of the current DC voltage if the current voltage is less than or equal to the predetermined voltage level; and (c) decreasing the current leading phase angle of the current DC voltage by a first predetermined level if the measured leading phase angle is greater than zero.
 52. The method of claim 51, further comprising the steps of: (d) measuring a current pulse width modulation (PWM) duty if the measured leading phase angle is equal to zero; and (e) decreasing the current PWM duty by a second predetermined level if the measured PWM duty if greater than zero.
 53. The method of claim 52, wherein the first predetermined level is equal to the second predetermined level.
 54. The method of claim 52, further comprising the steps of: (f) determining whether the motor is stopped; and (g) repeating steps (a) to (e) if it is determined in step (f) that the motor is not stopped.
 55. The method of claim 51, further comprising the steps of: (f) determining whether the motor is stopped; and (g) repeating steps (a) to (c) if it is determined in step (f) that the motor is not stopped.
 56. A control system for a motor-driven washing machine, the control system comprising: an electrical motor; a driving unit that applies an input voltage to the motor to drive the motor; a voltmeter that measures a reverse voltage generated by the motor for each predetermined period; and a microprocessor reducing a speed of the motor if the measured reverse voltage is less than or equal to a predetermined voltage level.
 57. The control system of claim 56, further comprising a timer that determines whether the each predetermined period has elapsed.
 58. The control system of claim 56, wherein the microprocessor is configured to measure a current leading phase angle if the measured reverse voltage is less than or equal to the predetermined voltage level, and to decrease the current leading phase angel by a first predetermined level if the measured leading phase angel is greater than zero.
 59. The control system of claim 58, wherein the microprocessor is further configured to measure a current pulse width modulation (PWM) duty if the measured leading phase angel is equal to zero, and to decrease the current PWM duty by a second predetermined level if the measured PWM duty is greater than zero.
 60. The control system of claim 59, wherein the first predetermined level is equal to the second predetermined level.
 61. A method of controlling a motor-driven washing machine, the method comprising the steps of: determining whether a command for a spin cycle is received from a user; and locking a washer door on the basis of whether a speed of a motor reaches a first predetermined speed if the spin cycle command is received, the motor rotating a washing tub containing a load of clothes to be dehydrated.
 62. The method of claim 61, wherein the step of locking the washer door comprises: increasing the motor speed from zero to the first predetermined speed to initiate the spin cycle; and generating a control signal to a door locking unit if the motor speed is equal to the first predetermined speed, the door locking unit locking the washer door upon receiving the control signal.
 63. The method of claim 62, further comprising the steps of: further increasing the motor speed from the first predetermined speed to a second predetermined speed; maintaining the motor speed of the second predetermined speed for a predetermined period for the spin cycle; and braking the motor in motion if the predetermined period is elapsed.
 64. The method of claim 62, wherein the first predetermined speed is 700 RPM and the second predetermined speed is 1000 RPM.
 65. The method of claim 61, wherein the command for the spin cycle is received from the user through a key input unit of the washing machine.
 66. A control system for a washing machine, the control system comprising: a washing tub containing a load of clothes to be dehydrated; an electrical motor rotating the washing tub if a command for a spin cycle is received from a user; and a microprocessor locking a washer door on the basis of whether a speed of the motor reaches a first predetermined speed.
 67. The control system of claim 66, wherein the microprocessor initially increases the motor speed from zero to the first predetermined speed, the microprocessor further generating a control signal to lock the washer door if the motor speed is equal to the first predetermined speed.
 68. The control system of claim 67, further comprising a door locking unit that locks the washer door upon receiving the control signal from the microprocessor.
 69. The control system of claim 66, further comprising a key input unit, through which the user inputs the command for the spin cycle.
 70. The control system of claim 66, wherein the first predetermined speed is 700 RPM.
 71. A method of controlling a motor-driven washing machine, the method comprising the steps of: determining whether a first current speed of a motor is less than a first predetermined speed if a motor-interruption of the motor is generated during a spin cycle, the motor rotating a washing tub containing a load of clothes to be dehydrated during the spin cycle; and braking the motor in motion by shorting power terminals of the motor for a first predetermined period if the first current speed is less than the first predetermined speed.
 72. The method of claim 71, further comprising the step of applying phase-reversed voltages to the power terminals for a second predetermined period if a second current speed of the motor is less than the first predetermined speed and greater than a second predetermined speed.
 73. The method of claim 72, further comprising the step of allowing a braking resistor connected to the motor to flow reverse currents generated by the motor so as to dissipate electrical power into heat if the second current speed of the motor is less than the first predetermined speed and greater than the second predetermined speed.
 74. The method of claim 72, further comprising the step of braking the motor by shorting the power terminals of the motor if a third current speed of the motor is less than the second predetermined speed.
 75. The method of claim 71, wherein the motor-interruption of the motor is generated when a user directly inputs a command for braking the motor or opens a washer door.
 76. A control system for a washing machine, the control system comprising: a washing tub containing a load of clothes to be dehydrated; a motor rotating to the washing tub during a spin cycle; and a microprocessor braking the motor shorting power terminals of the motor if a motor-interruption is generated during the spin cycle and if a first current speed of the motor is less than a first predetermined speed.
 77. The control system of claim 76, wherein the microprocessor further brakes the motor by applying phase-reversed voltage to the power terminals for a second predetermined period if a second current speed of the motor is less than the first predetermined speed and greater than a second predetermined speed.
 78. The control system of claim 77, wherein the microprocessor allows a braking resistor connected to the motor to flow reverse currents generated by the motor if the second current speed of the motor is less than the first predetermined speed and greater than the second predetermined speed.
 79. The control system of claim 77, wherein the microprocessor further brakes the motor by shorting the power terminals of the motor if a third current speed of the motor is less than the second predetermined speed.
 80. The control system of claim 76, wherein the motor-interruption of the motor is generated when a user directly inputs a command for braking the motor or opens a washer door.
 81. A circuit for limiting a motor current in an electrical appliance, the circuit comprising: a first resistor and a dip switch connected between a power source and a ground in series, the dip switch comprising a plurality of resistors having different resistances; a capacitor connected to the dip switch in parallel; an op amplifier having an inverting input connected to a node between the first resistor and the dip switch; and a third resistor connected between an noninverting input of the op amplifier and a ground, wherein any one of the plurality of resistors of the dip switch can be conveniently selected for limiting a current that flows through the third resistor.
 82. A method of controlling a motor-driven washing machine having a motor and a pair of a transistor and a braking resistor connected to the motor in parallel for limiting the reverse voltages generated by the motor during a motor brake, the resistor being connected to the transistor in series, the method comprising the steps of: measuring a voltage of a node between the transistor and the braking resistor; displaying a warning message indicating that the brake resistor is in an inoperative condition if the measured voltage is equal to zero; repeating the step of determining if a command for a wash cycle is received; and initiating the wash cycle if the measured voltage of the node is not equal to zero.
 83. The method of claim 82, further comprising the step of generating a warning sound if the measured voltage is equal to zero.
 84. A control system for a washing machine, the control system comprising: a motor rotating a wash tub or an agitator of the washing machine; a driving unit that drives the motor by applying input voltages to the motor; a pair of a braking resistor and a transistor connected to the driving unit in parallel, the transistor being connected to the braking resistor in series; a voltmeter measuring a voltage of a node between the transistor and the braking resistor; and a microprocessor generating a warning signal if the measured voltage of the node is not equal to zero.
 85. The control system of claim 84, further comprising a display unit displaying a warning message upon receiving the warning signal, the warning message indicating that the brake resistor is in an inoperative condition.
 86. The control system of claim 84, further comprising a sound generating unit generating a warning sound upon receiving the warning signal. 